(a) HHG spectrum from AI-based 3D-TDSE macroscopic simulations as a function of helium percentage in the gas jet. The left end corresponds to pure argon (100% Ar), while the right end represents pure helium (100% He). Time-frequency analyses for two specific mixtures are shown in b) η_% = 85 (85% He/15% Ar) and (c) η_% = 96.4 (96.4% He/3.6% Ar). In the latter, a modulation appears in the central attosecond burst (highlighted with a white dashed contour), which is further analyzed in the following panels. (d) HHG spectrum filtered within the temporal window of the central burst shown in (c), applied across a reduced range in (a). Panels (e) and (f) display the filtered spectra for the two specific mixtures: (e) η_% = 85 and (f) η_% = 96.4. In (f), a pronounced minimum near the 30th harmonic order is clearly observed.